As an liquid injection device having a liquid injection head capable of jetting a liquid under the state of microscopic liquid droplets, an image recording apparatus such as an inkjet printer that records images on a recording sheet, for example, is equipped with a liquid injection head having plural recording heads which jet ink droplets, and thereby, it is capable of printing images processed by a computer under the multicolor and multicontrast conditions, and is in widespread use as an output device for the computer.
For this recording head, piezoelectric elements are used as drive elements for jetting ink droplets, and when a plurality of piezoelectric elements provided corresponding to plural nozzles are driven selectively, ink droplets are jetted from the nozzles based on dynamic pressure of each piezoelectric element to stick to a recording sheet, thus a dot is formed, and intended printing is carried out. In recent years, the number of recording heads to be used for the image recording apparatus of this kind has been increased, for improving print resolution and a recording speed.
In this case, each piezoelectric element is driven based on the drive waveform in a prescribed form amplified up to the prescribed voltage, so that an ink droplet may be jetted from each nozzle in a necessary amount of ink droplet. Therefore, it is necessary to drive the piezoelectric element accurately at a prescribed voltage, for recording superior images with high image quality. However, since the piezoelectric element has generally fluctuations caused by differences of physical properties and processes, a different recording head, or a different nozzle even of the same recording head, needs voltage which is required for the different recording head or for the different nozzle. Further, different physical properties (viscosity and surface tension or the like) of a liquid such as jetted ink need different voltages.
Therefore, in the conventional voltage control device controlling drive of a recording head (for example, the voltage control device described in Japanese Patent Publication Open to Public Inspection No. 11-58735), it is possible to conduct calibration wherein voltage after the drive waveform to be applied on a recording head is amplified up to prescribed voltage is read, and the voltage is judged whether it is amplified accurately up to the prescribed voltage or not, and when it is not amplified to the prescribed voltage, a correction value for correcting its difference is calculated, and voltage based on the correction value is established newly, so that the piezoelectric element may be driven accurately at the prescribed voltage, and it has the structure shown in FIG. 9.
In FIG. 9, the numeral 100 represents a voltage controller, and voltage established by this voltage controller 100 is boosted by voltage amplifying sections 101 and 101 on the rear step to the prescribed voltage. Voltages boosted by the voltage amplifying sections 101 and 101 are sent to waveform amplifying sections 103 and 103 where the prescribed drive waveform generated in waveform generating section 102 is amplified to the voltage boosted by voltage amplifying sections 101 and 101 to be applied on each recording head 104, thus, a piezoelectric element of each recording head 104 is driven to jet ink droplet.
When voltage adjustment is conducted in this case, voltage immediately after being boosted by voltage amplifying sections 101 and 101 is read by voltage reading section 105 composed of AD converter, and is compared with the voltage established in advance, in voltage controller 100. As a result, when a difference from the voltage established in advance is caused, a correction value to correct the difference is calculated, and is stored in correction value storing section 100a in the voltage controller 100. Then, in the case of driving, the new voltage based on the correction value is established as correction voltage.
In the conventional voltage control device, the voltage immediately after being boosted by each of the voltage amplifying sections 101 and 101 is read, and voltage supplied to recording heads 104 and 104 is controlled based on the results of reading the aforesaid voltage.
However, the read step where voltage is read by voltage reading section 105 as stated above, is provided with waveform amplifying sections 103 and 103 for generating drive signals applied actually on recording heads 104 and 104, thus, a portion of fluctuation by amplification in this case is not considered in the voltage read by voltage reading section 105. Therefore, the voltage read by the voltage reading section 105 is one different from voltage applied on recording heads 104 and 104 actually through waveform amplifying sections 103 and 103.
Accordingly, even if the voltage adjustment is carried out based on the voltage acquired through reading by voltage reading section 105, correction is made under the reference of voltage that is different from voltage applied actually on each of recording heads 104 and 104, which makes it impossible to establish correct voltage, and causes dispersion in jetting ink droplets, resulting in a cause to decline image quality.
Therefore, when controlling voltage of recording heads 104 and 104, it is desired to conduct voltage adjustment by reading voltage immediately before applying on recording heads 104 and 104. However, for reading the voltage immediately before applying on recording heads 104 and 104, it is required to read voltage of drive waveform in a complicated form combined with a drive waveform generated in waveform generating section 102, which has caused a problem that the structure for reading voltage is complicated.
For example, in the case of a liquid injection head of a shear mode type wherein a side wall of a channel for reserving a liquid is formed with piezoelectric elements, and the side wall is deformed to the doglegged shear to give pressure for jetting a liquid in the channel, a rectangular drive waveform light that shown in FIG. 4(a) is sometimes used. In the case of the drive signals acquired by amplifying the aforesaid drive waveform up to the prescribed voltage, a period of time t for maintaining the maximum voltage Vmax is only about 2 μs, which makes it difficult to read voltage value accurately in such a short time, and requires a high speed reading device, resulting in a problem of a factor of cost increase.
There is further available a method to read the voltage before conducting waveform amplification by combining drive waveform and voltage. However, in the voltage which is read out by the aforesaid method, an amount equivalent to waveform amplification fluctuations after combining with drive waveform is not considered, and therefore, even when voltage correction is made based on the voltage thus read out, the correction is made under the reference of voltage which is different from voltage which is actually applied on a liquid injection head and has an amount equivalent to waveform amplification fluctuations, whereby, correct voltage cannot be set.
On the other hand, in the case of an image recording apparatus having a plurality of liquid injection heads, it is desired that voltage correction is conducted by distinguishing those requiring voltage correction from those requiring no voltage correction easily, because each of liquid injection heads needs to be corrected in terms of voltage individually. The problem of this kind is the same for the occasion where each of plural nozzles of a liquid injection head needs to be corrected in terms of voltage individually.
Japanese Patent Publication Open to Public Inspection No. 2006-95864 discloses a technology wherein signals for adjustment other than signals for jetting are used to solve characteristics dispersion in plural drive signal generating sections such as that for forming large dots, that for forming medium dots and that for forming small dots. However, there is no disclosure for a technology to conduct voltage correction individually for plural liquid injection heads or for plural nozzles.
Further, when obtaining a correction value from the voltage thus read out, it is desired that an accurate correction value having no dispersion is calculated.
With the aforesaid background, problems of the invention is to provide a voltage control device of a liquid injection head, a voltage control method and a liquid injection device of a liquid injection head, wherein voltage including an amount of amplification amplified in terms of waveform under the state immediately before being applied on a liquid injection head can be measured by a simple structure, thereby, voltage can be controlled accurately, accurate correction value having no dispersion can be calculated, and reliability of voltage control is high.